Photosensitive or photoreactive polymers are commonly used in coatings which have properties that can change when exposed to suitable radiation. Such a change in properties is usually a change in solubility and results in a sharp distinction between exposed and unexposed areas. Photocross-linking and photoinitiated polymerization are commonly used to exploit the photosensitivity of materials. This invention relates to photocross-linking between ethylenically unsaturated sites. Exposure to light of the photosensitive or photoreactive material results in a solubility change and creation of the image in the exposed material. Most commonly, resist images are produced by solvent development of photoinduced cross-linking (negative processing). Photoresist polymer compositions must satisfy a number of physical property dependent requirements under practical working conditions. The most important, and most difficult, requirements to fulfill are image discrimination, thermal stability, ink resistance and etch resistance when exposed. For image discrimination, the developing solvent must remove the soluble portion of the exposed material without distorting or swelling the insoluble areas to give a sharp true image.
Exposure of the photopolymer to light generally provides energy necessary to cross-link adjacent polymeric molecules. In many instances, this provides for a three dimensional cross-linked polymer. For example, with sufficient exposure to light, a polymer having diazo units becomes hydrophobic. A variety of photo-chemical systems have been used in photoresist applications including cinnamates, chalcones, p-azidophenyls, azidophthalates, p-phenylene, bis(acrylates), and many others.
There are a number of examples in the art of photosensitive compounds which have pendant pyridinium groups. Mino et al., Japanese Laid Open Patent Application No. Showa 61-186955 (1986) and Toyofuku et al., Japanese Laid Open Patent Application No. Showa 59-154442 (1984) both disclose the use of a polyvinyl alcohol backbone with side groups of the formula: ##STR2##
wherein R.sub.1, R.sub.2, n and Y are as defined in the reference.
Yanagi et al., Japanese Laid Open Patent Application No. Showa 55-135834 (1984) also teaches the use of side groups containing terminal substituted pyridinium groups, as shown in the formulae: ##STR3##
wherein n, m and X are as defined in the reference.
Yanagi also discloses the use of side chains with terminal styryl and substituted styryl groups, as shown in the formulae: ##STR4##
wherein n, m and X are as defined in the reference.
Yanagi continues by displaying a side chain with a terminal furanyl group, as shown here in the formula: ##STR5##
wherein n, m and X are as previously defined.
Ichimura et al., U.S. Pat. No. 4,925,770, also discloses the use of furanyl containing molecules. However, Ichimura teaches the inclusion of such a molecule freely in solution, rather than grafted to a backbone. Ichimura teaches a free molecule of the formula: ##STR6##
wherein R.sub.1 and R.sub.2 are as defined in the reference.
Engraving images on materials such as glass, metal and plastic traditionally involve the steps of first forming a resist layer containing an image and then sandblasting the entire surface. Any areas not covered by the resist are etched away to form an image while the protected areas remain intact. When imaging glass, a hydrofluoric acid treatment can substitute for sandblasting. In contrast, an aqueous solution of ferric chloride can be used if processing copper plate.
An example of this process is given by Suzuki et al., U.S. Pat. No. 5,427,890, who teach the use of a photosensitive laminate film to form the resist layer. The laminate film includes a water-soluble resin composition which exhibits photocrosslinkability. The areas exposed to light become insoluble in water while the protected portions remain water soluble. A water rinse is sufficient to remove the soluble portions to form the resist layer. While a number of possible photosensitive materials are known in the art, Suzuki is limited to the use of stilbazolium groups as the photosensitive moiety.